This invention relates generally to vision systems and more particularly to a method and system for regulating a signal level in a power supply for a radiation detector.
There are numerous radiation detectors. One type of detector employs an image intensifier tube and is used in night vision devices to amplify light and allow a user to see images in very dark conditions. Night vision devices typically include a lens to focus light onto the light receiving end of an image intensifier tube and an eyepiece at the other end to view the enhanced imaged produced by the image intensifier tube.
Modern image intensifier tubes use photocathodes. Photocathodes emit electrons in response to photons impinging on the photocathodes. The electrons are produced in a pattern that replicates the original scene. The electrons from the photocathode are accelerated towards a microchannel plate. A microchannel plate is typically manufactured from lead glass and has a multitude of microchannels, each one operable to produce a cascade of secondary electrons in response to an incident electron.
Therefore, photons impinge on the photocathode producing electrons which are then accelerated to a microchannel plate where a cascade of secondary electrons are produced. These electrons impinge on a phosphorous screen, producing an image of the scene.
The electrons are accelerated from the photocathode to the microchannel plate and from the microchannel plate to the phosphorous screen by electrostatic fields in the image intensifier. These electrostatic fields are established by power supplies to the photocathode, the microchannel plate and the screen. A conventional power supply for a microchannel plate has a relatively high output impedance. In addition, the current drawn by the microchannel plate varies strongly as a function of temperature and as a function of the average brightness of the image. Thus, the voltage across the microchannel plate varies strongly as a function of temperature and as a function of average image intensity if the voltage to the microchannel plate is unregulated.
A conventional power supply to a microchannel plate generates an oscillating signal that is fed into a transformer, with the output of the transformer being applied to a voltage multiplier. The output of the voltage multiplier is then applied to the microchannel plate. This voltage applied to the microchannel plate is generally regulated through the use of a feedback signal generated by a separate winding of the transformer. This feedback signal is scaled down and compared to a reference voltage, generating an error signal which is used to modify the oscillator amplifier that drives the transformer.
This conventional method of regulating the voltage has several drawbacks. One drawback is that a separate transformer is generally required to generate and control the voltage applied to the microchannel plate. A separate transformer increases cost, reduces reliability and reduces power supply efficiency for the image intensifier. A second drawback is that load regulation is very poor due to the relatively high output impedance of the voltage multiplier coupled with the fact that a separate transformer winding is used for feedback, with its independently associated temperature drift.
Recently, an improved voltage regulator was described in U.S. Pat. No. 5,883,381. This voltage regulator utilizes high-side control whereby the voltage is regulated with a variable impedance element in series with the output of a voltage multiplier. However, this high-side series voltage regulator is cumbersome, requiring relatively large components and a high parts count.
In accordance with the present invention, the disadvantages and problems associated with previous microchannel plate power supplies have been substantially reduced or eliminated. In particular, the present invention provides an improved method and system for regulating a signal level in an image intensification power supply.
In one embodiment, a method is provided for regulating a signal level in a power supply for a microchannel plate in a radiation detector. The method includes receiving an input signal at a signal multiplier. The signal multiplier has an output terminal and a return terminal. An output signal is produced at the output terminal. The output signal is provided to the microchannel plate. A regulation signal is provided from the output terminal to the return terminal. A signal level of the output signal is regulated with the regulation signal.
In accordance with another embodiment, a signal regulator for regulating a signal level in a power supply for a microchannel plate in a radiation detector is provided. The signal regulator includes a signal multiplier. The signal multiplier has a first input terminal, a second input terminal, an output terminal, and a return terminal. A transformer has a first terminal coupled to the first input terminal of the signal multiplier and a second terminal coupled to the second input terminal of the signal multiplier. The transformer is operable to drive an input signal into the signal multiplier. An error integrator is coupled to the output terminal of the signal multiplier. A reference circuit and a drive are coupled to the error integrator. A variable impedance is coupled to the return terminal of the signal multiplier and is coupled to the drive. The drive is operable to adjust a level of the variable impedance. The variable impedance is operable to regulate an output signal produced at the output terminal of the signal multiplier.
Technical advantages of the present invention include providing an image intensification power supply with an improved regulator for a signal level. In particular, the voltage across the microchannel plate is regulated without requiring a separate transformer. In addition, fewer components, including a reduced number of high voltage components, are required in comparison with existing voltage regulators. As a result, cost and size are reduced, reliability and response time are improved, and the image intensifier power supply is made more efficient.
Other technical advantages of the present invention will be readily apparent to the those skilled in the art from the following figures, description and claims.